The present disclosure relates to a machine for compression molding plastic articles, such as closure shells or sealing liners within closure shells, and more particularly to an apparatus for placing mold charges into the molds of the compression molding machine.
Machines for compression molding closure shells, or compression molding sealing liners within closure shells, typically include a turret or carousel that rotates around a vertical axis. A plurality of molds are provided around the periphery of the carousel, in the form of male and female mold sections that are aligned along vertical axes parallel to the axis of rotation. Cams drive one or both of the mold sections of each pair between an open position, in which a molded part is stripped from the mold and a charge of molten plastic material is placed into the mold, and a closed position in which the mold sections are brought together to compression mold the shell or liner. In a liner machine, premade shells are placed in a nest when the mold sections are open, and a charge or pellet of liner material is placed within the mold before the mold is closed. U.S. patents that illustrate machines of this type for compression molding plastic closure shells include U.S. Pat. Nos. 5,670,110, 5,989,007, 6,074,583 and 6,478,568. U.S. patents that illustrate machines of this type for compression molding sealing liners within closure shells include U.S. Pat. No. 5,451,360. U.S. application Ser. No. 11/109,374 discloses a vertical wheel compression molding machine, which rotates around a horizontal axis, for compression molding closure shells or sealing liners within closure shells.
The present disclosure involves a number of aspects that can be implemented separately from or in combination with each other.
An apparatus for placing mold charges into a mold of a compression molding machine, in accordance with one aspect of the present disclosure, includes at least one mold charge pick-up cup for receiving a severed charge of molten plastic, a vacuum source for applying a vacuum to the pick-up cup to retain the mold charge in the cup, and a source of gas (such as air) under pressure for periodically applying gas to the cup to release the mold charge from the cup. In one exemplary embodiment, the vacuum source applies a continuous vacuum to the cup, and the source of gas under pressure periodically applies gas to the cup to overcome the continuous vacuum at the cup. In another exemplary embodiment, vacuum and gas under pressure, are alternately applied to the cup. The vacuum source preferably includes a vacuum generator coupled to the source of gas under pressure for generating the vacuum to be applied to the cup. The source of gas under pressure preferably includes a valve for periodically applying gas under pressure to the cup. The apparatus preferably includes a carrier for moving the cup from a source of severed charges of molten plastic to the mold of the compression molding machine, with the cup, the vacuum pump and the valve preferably being mounted on the carrier. The vacuum source preferably includes a vacuum limiter that also is mounted on the carrier.
The mold charge pick-up cup, in accordance with another aspect of the present disclosure, preferably is of annular bellows-shaped construction having a central axis. The bellows-shaped pick-up cup is resiliently bendable laterally of its central axis and resiliently compressible longitudinally of its axis to enhance pick-up of the mold charge and application of vacuum to the mold charge to carry the mold charge to the mold of the compression molding machine. The pick-up cup of annular bellows-shaped construction preferably is of elastomeric construction, most preferably silicone construction.